Why he could be the Zodiac:
Earl Van Best, Jr. is the subject of FX's The Most Dangerous Animal of All, and it was his son, Gary Stewart, who worked with experts to compile the evidence against his birth father. Van Best was 27 when he met Stewart's mother, Judith Gilford, who was 14, at a San Francisco ice cream parlor. He married Gilford and she became pregnant with Stewart, but he was soon arrested for pedophilia, fraud, rape, drunk driving, and other charges, per The Chronicle.
Stewart, who was adopted, first noticed that his biological father had a strong likeness to the police sketch of the Zodiac killer. Additionally, he claims that Van Best was interested in cryptography like the killer, and the musicals of Gilbert and Sullivan (another favourite of the Zodiac). He also reportedly lived two blocks from the murder site of one of the Zodiac's victims, Paul Stine. His most compelling evidence came in the form of a handwriting analysis that allegedly matched Van Best's handwriting to the writing in the letters that were sent by the Zodiac to the San Francisco police and newspapers.
Why he's probably not the killer:
The evidence that Van Best could be the Zodiac is entirely circumstantial. And while Stewart stands by the handwriting analysis which is based on his parents' marriage certificate, a manager at the church where they were wed said that the priest filled out all of the documents, per The Chronicle.